So far I've watched Manster
and Five Million Years to Earth/Quatermass and the Pit
live and recorded the others I was interested in. Manster
was basically just B-movie schlock, though being a Japanese co-production gave it an interesting edge.
But I really liked the Quatermass film (the first one I've ever seen as far as I recall, though I've certainly heard of the character). It was a smart, solid SF story with an underlying message about intolerance (I thought the genocidal Martians were a Nazi allegory, but after reading up on Wikipedia I see it was really more about race riots in England). And it had some lovely touches of naturalism -- like Dr. Roney giving a speech in the Underground and having to wait awkwardly when a train roared by just as he was starting to make his important point. Or the bit where the scholar translating the ancient Latin text turned the page and then had to turn back to check a word on the previous page -- since word order isn't always the same in different languages. What marvelous attention to detail! It got a little more erratic toward the end, though; at times the pacing of the scenes seemed a bit off (like the cutaway to the reporter on the pub TV getting cut off as things got erratic coming just before things actually started to get erratic), and some bits of the climactic action were a bit hard to follow. And the ending was a little abrupt; I gather the original serial had a speech at the end that underlined the message more clearly.
And I can definitely see how Quatermass was an influence on Doctor Who
in the '70s. This did almost feel like a prototypical Third Doctor/UNIT story, though Colonel Breen turned out to be a lot more antagonistic than the Brigadier ever was.